In an internal mixer of the related art, a tangential rotor (mixing rotor) is employed when there is a need to maintain a large mixing capacity in order to improve the productivity of the internal mixer for producing a mixed material (for example, see Patent Document 1). In the internal mixer of the related art that employs the tangential rotor, it is difficult to transmit high specific energy (mixing energy per unit weight of a material to be mixed) to the material to be mixed in a short time. For this reason, a method is used which increases the mixing time in order to mix the material to be mixed as one in a desired mixed state.
However, with the method of increasing the mixing time, the temperature of the material to be mixed increases with the passage of the mixing time. On the other hand, there is a limit to temperatures such as a temperature of preventing the degradation of the material to be mixed and a predetermined reaction temperature for the material to be mixed. In these circumstances, for the internal mixer using the tangential rotor of the related art, there is often a case in which the number of rotations of the rotor needs to be decreased after the mixing time reaches certain time in order to prevent the temperature of the material to be mixed from exceeding the temperature limit. As described above, problems with the related art include the extended mixing time and the decreased number of rotations of the rotor. As a result, a problem arises that the productivity does not improve due to the influence thereof.
Accordingly, a mixing rotor is also developed which may perform a low-temperature mixing operation and improve the mixing quality, as compared to the rotor disclosed in Patent Document 1, by exercising ingenuity in the shape, the arrangement or the like of blades (for example, see Patent Document 2). However, there is a room for improvement in the productivity of the mixing rotor for producing the mixed material.
Specifically, in the tangential hermetically sealed, even when there is an attempt to transmit high specific energy to the material to be mixed in a short time by decreasing the weight of the material to be mixed input into the chamber so as to increase the amount of the mixing energy transmitted to the material to be mixed per unit weight of the material to be mixed, the mixing energy is not easily transmitted to the material to be mixed due to the influence of a decrease in the charging rate of the material to be mixed inside the chamber. For this reason, the mixing time may not be noticeably shortened, and the weight of the material to be mixed input per batch decreases. Accordingly, the productivity of the mixer of the related art for the mixed material does not improve as expected.
Further, in such a tangential internal mixer, in order to shorten the mixing time by promptly increasing the homogeneity of the material to be mixed inside the chamber, a method is also used which increases the torsion angle of each blade with respect to the rotor axial line in order to cause the active flow of the material to be mixed in the rotor axis direction. However, when the torsion angle increases, the amount of the material to be mixed flowing toward the rear surface of the blade over the top portion (also referred to as “tip portion” or “land portion”) of the blade increases. For this reason, there is an effect of improving the flow of the material to be mixed in the rotor axis direction, but the effect is low. That is, the flow of the material to be mixed in the rotor axis direction does not increase noticeably. As a result, with such a method, the mixing time is not so drastically improved.